I'm not sure I follow what would be dangerous in my case, but I guess I'll go with opto-isolators. Thanks for replying.
Also, I've been using relays with 5V input to close a 230V connection with inductive load (btw I see the need for optoisolators in this case) - but I've never used a relay with 24V to control 5V.
Is it normal practice to use a relay to step down the signal voltage like this?